The present invention relates to end-capped polyfluorenes, films and devices based thereon.
In recent years much attention has been paid to polymers being useful for incorporation into field-effect transistors, light-emitting diodes (LEDs) and photo-voltaic devices. A wide variety of polymers have been included as active media in these electronic devices. A class of compounds that has been found to be potentially useful for such purpose are the polyfluorenes.
Various reasons support the use of polyfluorenes in these devices: First of all, polyfluorenes are displaying impressive blue-emission properties and because of this they received considerable attention with respect to their potential for inclusion into emission layers of LEDs. Several reports have demonstrated bright blue emission from polyfluorene homopolymers (A. W. Grice; D. D. C. Bradley; M. T. Bernius; M. Inbasekaran; W. W. Wu; E. P. Woo; Appl. Phys. Lett. 1998, 73, 629; Y. Yang and Q. Pei; J. Appl. Phys. 81, 3294 (1997)).
A second important property of polyfluorenes, in particular polyfluorene homopolymers, is their thermotropic liquid-crystalline behaviour, which allows to orient these polymers on alignment layers, for example rubbed polyimide layers (M. Grell, D. D. C. Bradley, M. Inbasekaran, E. P. Woo, Adv. Mater. 9, 798 (1997); M. Grell, D. D. C. Bradley, X. Long, T. Chamberlain, M. Inbasekaran, E. P. Woo, M. Soliman, Acta Polym. 49, 439 (1998)). Orientation of the polymers on such alignment layers enables the emission of linearly polarized light which is particularly useful for devices such as liquid-crystal (LC) displays in which emission layers incorporating polyfluorene are being used as backlights. LEDs emitting linearly polarized light and having a dichroic ratio in emission of more than 20 and a brightness in excess of 100 cd/m2 could be fabricated when the polyimide layers were doped with appropriate hole-transporting molecules (M. Grell, W. Knoll, D. Lupo, A. Meisel, T. Miteva, D. Neher, H. G. Nothofer, U. Scherf, H. Yasuda, Adv. Mater. 11, 671 (1999).
The efficiency of devices based on non-aligned and aligned polyfluorenes is, however, still far too low for applications. The efficiency of a bilayer device comprising a cross-linked hole-transporting layer (HTL) and an emission layer (EML) based on poly(9,9-bis(n-octyl)fluorene-2,7-diyl) (PFO) with linear octyl side-chains was only 0.25 cd/A (A. W. Grice; D. D. C. Bradley; M. T. Bernius; M. Inbasekaran; W. W. Wu; E. P. Woo; Appl. Phys. Lett. 73, 629 (1998)). Devices with aligned polyfluorenes, using poly(9,9-bis(2-ethylhexyl)fluorene-2,7-diyl) are reported to show an even lower efficiency of approximately 0.12 cd/A (M. Grell, W. Knoll, D. Lupo, A. Meisel, T. Miteva, D. Neher, H. G. Nothofer, U. Scherf, H. Yasuda, Adv. Mater. 11,671 (1999)).
Several attempts have been made to chemically modify polyfluorenes in order to increase the device efficiency. For example Kim et al. (Macromolecular Symposia, 1999, 143, 221-230) copolymerized 2,7-diethynyl-9,9xe2x80x2-di-n-hexylfluorene and 2,7-dibromo-9,9xe2x80x2-di-n-hexylfluorene to yield poly(9,9xe2x80x2-di-n-hexyl-2,7-fluorenyleneethynylene). The alternating copolymer emitted blue colour with a peak maximum at 475 nm on excitation either at 340, 365 or 400 mn. The principle emission maximum shifted to 425 nm on excitation at 340 nm when the polymer was blended with polyvinylcarbazole (PVK). Light-emitting diodes (LEDs) fabricated with the alternating copolymer sandwiched between indium-tin oxide glass and Al emitted a light with a peak maximum at 550 nm. The peak maximum shifted to 425 nm when the copolymer was blended with PVK with the blending ratios between 5 to 20% of the emissive copolymer.
Colour tuning was deliberately achieved via incorporation of benzothiadiazole, perylene or anthracene moieties (Klaerner, G.; Davey, M. H.; Chen, W. D.; Scott, J. C.; Miller, R. D.; Adv. Mater. 10, 993 (1998); M. Kreyenschmidt, G. Klxc3xa4rner, T. Fuhrer, J. Ashenhurst, S. Karg, W. D. Chen, V. Y. Lee, J. C. Scott, R. D. Miller, Macromolecules 31, 1099 (1998); Y. He, S. Gong, R. Hattori, J. Kanicki, Appl. Phys. Lett. 74, 2265 (1999)). The problem, however, with the inclusion of such chemical moieties into the polyfluorene main chain or the copolymerization with other monomers is the inevitable modification of essential properties of the main chain such as the stiffness and the geometrical shape, thereby inadvertently altering the character of the polyfluorene, e. g. its liquid-crystalline behaviour, if such had been present before any modification.
Another problem with LED-devices based on polyfluorene emission layers is that the emission spectrum of such an LED exhibits a significant contribution of longer wavelengths, particularly in the range of the red part of the spectrum (M. Grell, D. D. C. Bradley, X. Long, T. Chamberlain, M. Inbasekaran, B. P. Woo, M. Soliman; Acta Polym. 49, 439 (1998); M. Grell, W. Knoll, D. Lupo, A. Meisel, T. Miteva, D. Neher, H. G. Nothofer, U. Scherf, H. Yasuda, Adv. Mater. 11, 671 (1999); J. Teetsov, M. A. Fox; Journal of Materials Chemistry 9, 2117 (1999), V. N. Bliznyuk, S. A. Carter, J. C. Scott, G. Klxc3xa4rner, R. D. Miller, and D. C. Miller; Macromolecules 32, 361 (1999)). The strength of this contribution changes strongly with the molecular weight and the nature of the side chains. This situation is aggravated by the fact that the alignment of the polymer in the liquid-crystalline state requires an annealing step at higher temperatures enhancing this undesired red contribution. Several attempts have been made towards a control of red-shifted emission bands. These include the synthesis of statistical (M. Kreyenschmidt, G. Klxc3xa4rner, T. Fuhrer, J. Ashenhurst, S. Karg, W. D. Chen, V. Y. Lee, J. C. Scott, R. D. Miller; Macromolecules 1998, 31, 1099) or block (D. Marsitzky, M. Klapper, K. Mxc3xcllen; Macromolecules 1999, 32, 8685) copolymers, the attachment of sterically demanding groups (G. Klxc3xa4rner, R. D. Miller, C. J. Hawker; Polym. Prepr. 1998, 1006) or thermal cross-linking of terminal reactive groups, e. g. benzocyclobutane ((a) E. P. Woo, M. Inbasekaran, W. Shiang, G. R. Roof; Int. Pat. Appl. WO97/05184 (1997); (b) M. Inbasekaran, W. Wu, E. P. Woo; U.S. Pat. No. 5,770,070 (1998)) units or unsaturated functions (e. g. styryl) (Klaerner, G.; Davey, M. H.; Chen, W. D.; Scott, J. C; Miller, R. D.; Adv. Mater. 1998, 10, 993; G. Klxc3xa4rner, J.-I. Lee, V. Y. Lee, E. Chan, J.-P. Chen, A. Nelson, D. Markiewitz, R. Siemens, J. C. Scott, R. D. Miller; Chem. Mater. 1999, 11, 1800). In most of these cases the electronic properties as well as the phase behaviour have become severely altered compared to that of the polyfluorene homopolymers. For example the synthesis of block copolymers has in fact led to an even increased contribution of undesired red-shifted emission states (D. Marsitzky, M. Klapper, K. Mxc3xcllen; ibid.).
Accordingly, it is an object of the present invention to provide polymers useful for incorporation into electronic devices such as FETs, LEDs and photovoltaic devices which do not show any unwanted red-shift contribution. Particularly it is an object of the present invention to provide polyfluorenes useful for incorporation into these devices which do not show any undesired red-shift contribution. Another object of the present invention is to provide polymers, in particular polyfluorenes, that allow for the fabrication of electronic devices, in particular LEDs, FETs and photovoltaic devices with a higher efficiency. It is another object of the present invention to provide LEDs with a higher brightness, a lower onset voltage, a negligible red contribution, a better colour stability and the potential to achieve high dichroic ratios.
All these objects are solved by a polyfluorene end-capped with at least one charge-transporting moiety.
It is preferred that in such a polyfluorene the charge-transporting moiety is selected from the group comprising electron-transporting moieties, hole-transporting moieties and ion-transporting moieties, wherein, more preferably, the charge-transporting moiety is selected from the group comprising: 
wherein R1 and R2 are independently at each occurrence selected from the group comprising straight chain C1-20 alkyl, branched C1-20 alkyl, aryl, substituted aryl, alkylaryl, substituted alkylaryl, alkoxyaryl, substituted alkoxyaryl, aryloxyaryl, substituted aryloxyaryl, dialkylaminoaryl, substituted dialkylaminoaryl, diarylaminoaryl and substituted diarylaminoaryl, and
wherein R3 is independently at each occurrence selected from the group comprising straight chain C1-20 alkyl, branched C1-20 alkyl, aryl, substituted aryl, alkylaryl and substituted alkylaryl.
In one embodiment it is preferred that the polyfluorene comprises about 0.5-9 percent by weight of charge-transporting moieties.
It is also preferred that the polyfluorene comprises about 0.5-9 mole percent of charge-transporting moieties.
In a particularly preferred embodiment R1 and R2 are independently at each occurrence selected from the group comprising 4-methylphenyl, 2-methylphenyl, phenyl, 1-naphthyl, 2-naphthyl, 4-methoxyphenyl, 2-methoxyphenyl, 4-dimethylaminophenyl, 2-dimethylaminophenyl, 4-diphenylaminophenyl and 4-phenoxyphenyl.
Preferred combinations are:
a) R1=phenyl, R2=4-methylphenyl;
b) R1=phenyl, R2=1-naphthyl;
c) R1=phenyl, R2=2-naphthyl;
d) R1=R2=4-methylphenyl;
e) R1=R2=phenyl;
f) R1=R2=4-dimethylaminophenyl;
g) R1=R2=4-diphenylaminophenyl.
The objects of the invention are also solved by a polyfluorene end-capped with at least one moiety selected from the group comprising 
wherein R1 and R1 are independently at each occurrence selected from the group comprising straight chain C1-20 alkyl, branched C1-20 alkyl, aryl, substituted aryl, alkylaryl, substituted alkylaryl, alkoxyaryl, substituted alkoxyaryl, aryloxyaryl, substituted aryloxyaryl, dialkylaminoaryl, substituted dialkylaminoaryl, diarylaminoaryl and substituted diarylaminoaryl, and
wherein R3 is independently at each occurrence selected from the group comprising straight chain C1-20 alkyl, branched C1-20 alkyl, aryl, substituted aryl, alkylaryl and substituted alkylaryl.
In one embodiment it is preferred that the polyfluorene comprises about 0.5-9 percent by weight of charge-transporting moieties.
It is also preferred that the polyfluorene comprises about 0.5-9 mole percent of charge-transporting moieties.
In a preferred embodiment R1 and R2 are independently at each occurrence selected from the group comprising 4-methylphenyl, 2-methylphenyl, phenyl, 1-naphthyl, 2-naphthyl, 4-methoxyphenyl, 2-methoxyphenyl, 4-dimethylaminophenyl, 2-dimethylaminophenyl, 4-diphenylaminophenyl and 4-phenoxyphenyl.
Preferred combinations are:
a) R1=phenyl, R2=4-methylphenyl;
b) R1=phenyl, R2=1-naphthyl;
c) R1=phenyl, R2=2-naphthyl;
d) R1=R2=4-methylphenyl;
e) R1=R2=phenyl;
f) R1=R2=4-dimethylaminophenyl;
g) R1=R2=4-diphenylaminophenyl.
The objects of the present invention are further solved by a polyfluorene having the formula 
wherein R4 and R5 are independently at each occurrence selected from the group comprising: 
R1 and R2 being independently selected from the group comprising straight chain C1-20 alkyl, branched C1-20 alkyl, aryl, substituted aryl, alkylaryl, substituted alkylaryl, alkoxyaryl, substituted alkoxyaryl, aryloxyaryl, substituted aryloxyaryl, dialkylaminoaryl, substituted dialkylaminoaryl, diarylaminoaryl and substituted diarylaminoaryl,
R3 being selected from the group comprising straight chain C1-20 alkyl, branched C1-20 alkyl, aryl, substituted aryl, alkylaryl and substituted alkylaryl,
and wherein R6 and R7 are independently at each occurrence selected from the group comprising straight chain C1-20 alkyl, branched chain C1-20 alkyl, aryl, substituted aryl, alkylaryl, substituted alkylaryl, xe2x80x94(CH2)qxe2x80x94(Oxe2x80x94CH2xe2x80x94CH2)rxe2x80x94Oxe2x80x94CH3,
q being selected from the range 1xe2x89xa6qxe2x89xa610, r being selected from the range 0xe2x89xa6rxe2x89xa620,
and wherein L and M are independently at each occurrence selected from the group comprising thiophene, substituted thiophene, phenyl, substituted phenyl, phenanthrene, substituted phenanthrene, anthracene, substituted anthracene, any aromatic monomer that can be synthesized as a dibromo-substituted monomer, benzothiadiazole, substituted benzothiadiazole, perylene and substituted perylene,
and wherein m+n+oxe2x89xa710, each of m, n, o being independently selected from the range 1-1,000,
and wherein p is selected from the range 0-15,
and wherein s is selected from the range 0-15,
with the proviso that, if R4 is H, R5 is not H, and if R5 is H, R4 is not H.
In one embodiment a polyfluorene is preferred,
wherein m, p, s, o are 0, and
wherein R4-R7 and R1-R3 are as previously defined.
In one embodiment a polyfluorene is preferred which comprises about 0.5-9 percent by weight of R4- and R5-groups.
In one embodiment a polyfluorene is preferred which comprises about 0.5-9 mole percent of R4- and R5-groups.
It is preferred that a polyfluorene according to the present invention be cross-linked to a polyfluorene according to the present invention via at least one linkage selected from the group comprising a 9,9-spirobifluorene-linkage, a bifluorenyl-linkage, a bifluorenylidene-linkage and an xcex1,xcfx89-difluorenylalkane-linkage with a length of the alkane spacer in the range from 1-20 C-atoms.
It is also preferred that a polyfluorene according to the present invention has at least one color-tuning moiety incorporated into the main chain, wherein, more preferred, the color-tuning moiety is selected from the group comprising thiophene, substituted thiophene, phenyl, substituted phenyl, phenanthrene, substituted phenanthrene, anthracene, substituted anthracene, any aromatic monomer that can be synthesized as a dibromo-substituted monomer, benzothiadiazole, substituted benzothiodiazole, perylene and substituted perylene.
In one embodiment a polyfluorene is preferred which is liquid-crystalline, wherein, more preferred, it is liquid-crystalline at or above 70xc2x0 C.
In another embodiment a polyfluorene is preferred, which is amorphous.
The objects of the present invention are furthermore solved by a polyfluorene selected from the group comprising 
wherein n is as previously defined.
The objects of the present invention are also solved by a film incorporating a polyfluorene according to the present invention.
It is preferred that the film be aligned.
It is preferred that the film incorporates at least one other substance, wherein said other substance is selected from the group comprising fluorescent dyes, hole-transporting moieties, electron-transporting moieties, ion-transporting moieties, phosphorescent dyes, nanoparticles, low molecular weight liquid-crystalline moieties, other liquid-crystalline and/or fluorescent and/or phosphorescent and/or charge-transporting polymers.
In one embodiment it is preferred that the film be deposited on an alignment layer.
In one embodiment the film has a thickness ranging from 10 nm to 2 xcexcm. In one embodiment it is preferred that the film has a thickness ranging from 50-300 nm.
The objects of the present invention are also solved by a device selected from the group comprising FETs, photovoltaic elements, LEDs and sensors, incorporating a polyfluorene according to the present invention.
It is preferred that the device has another polymer incorporated, wherein, more preferred, said polymer is a luminescent polymer.
The objects of the present invention are also solved by a device selected from the group comprising FETs, photovoltaic elements, LEDs and sensors, incorporating a film according to the present invention.
The objects of the present invention are also solved by the use of a polyfluorene according to the present invention in a film, wherein, more preferred, the film is an emission layer.
The objects of the present invention are also solved by the use of a polyfluorene according to the present invention in a device selected from the group comprising FETs, photovoltaic elements, LEDs and sensors.
The objects of the present invention are also solved by the use of a film according to the present invention in a device selected from the group comprising FETs, photovoltaic elements, LEDs, and sensors.
The objects of the present invention are also solved by the use of a device according to the present invention in combination with a liquid-crystal display (LCD).
It has surprisingly been found that end-capping a polyfluorene polymer main chain with charge-transporting moiety yields LEDs with a higher efficiency and a better colour stability, yet without altering the electronic properties of the polyfluorene polymer main chain. Furthermore, surprisingly, end-capping with appropriate charge-transporting groups does not disturb the phase property of the polyfluorene polymer and does not influence their orientational capabilities. A further advantage in connection with the present invention is the fact that end-capping the polyfluorene molecule with a charge-transporting moiety in the indicated weight-percent range or mole-percent range enables a precise control of the molecular weight of the polyfluorene.
The terms as used herein are defined as follows:
A molecule is xe2x80x9cend-capped withxe2x80x9d a group if the group is attached, preferably, covalently attached, to said molecule. The site of attachment can be any site in the molecule that renders the attached group a terminal group; in the case of a linear polymer the preferred site of end-capping are the two termini. Attachment-sites, however, other than the terminal sites are envisaged, too, such as attachment-sites for side chains. In a branched polymer the preferred sites for end-capping are the terminal sites of each branch of the polymer.
The term xe2x80x9ccharge-transporting moietyxe2x80x9d is meant to designate any chemical moiety capable of facilitating the transport of electrons, holes (e. g. charge-deficiencies, particularly electron-deficiencies) and ions. The term furthermore comprises also those groups, that can be transformed into electron-transporting moieties, hole-transporting moieties or ion-transporting moieties, e. g. by protonation, cleavage, proteolysis, photolysis etc.
A xe2x80x9ccolour-tuning moietyxe2x80x9d is any moietiy capable of modifying the spectral properties of a molecule to which such moiety is attached and/or into which such moiety is incorporated.
A xe2x80x9cfilmxe2x80x9d is any layer having a thickness selected from the range 10 nm-2 xcexcm, preferably selected from 50-300 nm. Such a film can, e. g., be an emission layer of an opto-electronic device, e. g. an LED. The film can be aligned or non-aligned and prepared by, for example, casting from solution, spin casting, doctor-blading, offset printing, inkjet printing etc. The alignment is preferably achieved by annealing through heating above or close to the transition temperature to the liquid-crystalline phase, but other methods and ways of annealing and aligning are possible, for example by exposition to solvent vapor. The film can be deposited on a specific alignment layer for the purpose of alignment of the molecules in the film, or it can be aligned directly by techniques such as stretching, rubbing etc. Preferable materials for an alignment layer are selected from the group comprising polyimide, nylon, PVA, poly(p-phenylene vinylene), polyamide, teflon (hot rubbed) and glass, but are not restricted thereto. The alignment layer can have its properties induced by rubbing, illumination with polarized light, ion-bombardment, surface-structure induction by grating etc. In a device according to the present invention a film according to the present invention can be used in conjunction with at least one other layer, e. g. another emission layer or several other emission layers, depending on the requirements of the application (in addition to the other layers whose presence is inherently essential for the proper functioning of the device).
The term xe2x80x9cin combination with a liquid-crystal displayxe2x80x9d is meant to designate any arrangement in which a film and/or a device according to the present invention is in physical proximity to a liquid-crystal display (LCD) and/or functionally coupled thereto, e. g. the use of an LED, preferably an LED emitting polarized light, as a backlight for a liquid-crystal display.